The present invention relates to a method and apparatus for spot coating on printing substrates in large size printing machines producing printed images by application of an ink layer on the printing substrates.
Spot coating on surfaces of printing substrates is usually made by printing plates, which are especially made for this purpose. These printing plates have partial recesses. This solution is described in the 9th edition of the book xe2x80x9cOffsetdrucktechnikxe2x80x9d (Offset printing) by Helmut Teschner on pages 11 to 43. This solution is not applicable for large size printing presses because the coating plates can not be manufactured in sufficient quality at such plate dimensions.
An object of the invention is to provide a method and apparatus for spot coating of printing substrates also applicable in large size printing presses.
xe2x80x9cThe present invention solves this and other problems by using a universally applicable offset plate to coat substantially the entire area of a printed image, wherein the coating reacts with ink layers of at least two ink systems thereby changing the printed image so that areas of varying gloss degrees are created. A printed offset plate may be used. The present invention uses a conventional printing press comprising at least two printing units for printing at least two ink systems, an optional dryer allocated to the printing units, and a coating unit for application of the final coating layer succeeding the printing units.xe2x80x9d
An advantage of the present invention is that varying degrees of gloss can be produced using only a single coating plate without partial recesses. The manufacturing cost for the coating plates decreased. The coating plate can now be used for several printing jobs so that the make ready time is reduced. Furthermore, only one coating unit or coating tower is required.